Weird spiky shadows around the edges of my walls
Something like that generates Sun light.

You can try to get rid of by Shadow - Cascade Shadow Map - Max Distance, but seems to be a tricky solution.

This effect is such visible when Lamp light is switched to Sun where Strenght of light is too high (1000). Lower value to 3 is ussually fine in most cases.


Edit
Later I noticed - light still penetrates the corners

Enable Contact Shadow subpanel and play a bit with values

... or, instead all of this, use another type of light :)